iseekool's posts are correct - that is the only way.
The trip computer software in Nissans is so inaccurate I wonder why they even bothered to put it in the car.
According to the unit in my 2010 370 (7speed) I have achieved 6.94 Lt/100Km.
Sure, I was getting really great economy but I doubt it was THAT good. And I was driving in such an unrealistic manner to get that number...
I live in the Snowy Mountains and work in Sydney so it is pretty much all highway running too.
I am still trying to determine if it has the same software that is in my 2008 Maxima (CVT) ...the fuel guage in that car doesn't actually measure the fuel you have but what it thinks you have based on usage rate. I have proved that if you can quickly drop the L/Km number the needle on the fuel guage goes up!
From Mittagong to Campbelltown is a drop in altitude of around 600metres so overall, a downhill run. If you reset the fuel usage at the top of Catherine Hill you will get a lower consumption number so the car makes a decision based simply on if you can go further....you must have more fuel in the tank!
Stupid and unreliable.